[homonculus1]

There aren't going to be fewer people as a result of this, there are just going to be fewer South Koreans in South Korea. When developed nations pursue non-procreative social policies and lose their demographics, they get internally replaced from undeveloped nations. The global population continues to grow.

[AlexandrB]

The growth of the global population is slowing[1]. Undeveloped nations are developing, and as they do their birth rate drops as well.

[1] https://www.macrotrends.net/countries/WLD/world/birth-rate